In the application of liquid fertilizers, liquid weed killers and other liquid chemicals to lawns of residences and commercial buildings, it is common to use a mobile vehicle such as a four wheel truck which carries one or more supply tanks for the fertilizer or other liquid chemicals. Each chemical is distributed or dispensed through a flexible hose extending from a hose reel mounted within the truck, and the outer end of the hose has a manually operated spray nozzle with a control valve. A liquid supply pump is commonly driven directly by a shaft connected to the power takeoff (PTO) of the truck engine. The pump has also been driven by a hydraulic motor which receives hydraulic fluid from a hydraulic pump driven from the PTO of the truck engine. The hose reel may also be driven or rotated by an electric motor or by a hydraulic motor connected to the hydraulic pump driven by the PTO, and controls are provided near the hose reel to control the hose reel motor.
In order to operate the liquid chemical supply pump at a site where lawn care services are desired, the truck engine is set to idle at a predetermined speed in order to provide continuous power to the chemical supply pump driven from the PTO of the truck engine. In a full day of operation of a typical lawn care truck, the engine may idle approximately six hours, consuming about one-half gallon of fuel per hour. Thus during a normal day of operation, an idling lawn care truck consumes about three gallons of fuel which would amount to approximately 600 gallons of fuel per year for 200 days of operation. At a cost of about $3.00 per gallon of fuel, an idling truck may consume approximately $1800 of fuel a year. In view of the fact that there is many thousands of lawn care trucks in use, the total cost for pumping liquid chemicals to a lawn is very substantial.
It has been known to operate a liquid chemical supply pump using an electric motor driven supply pump supplied with electricity from the vehicle or truck electrical power system, for example, as disclosed in U.S. Pat. No. 4,236,673 and U.S. Pat. No. 6,164,560. However, use of an electric motor driven supply pump drains the vehicle electrical power system and does not permit the vehicle or truck engine to be shut down at successive lawn care sites which are in close driving distances. It has also been known to drive or operate the liquid chemical supply pump from a separate engine considerably smaller than the truck engine, for example, as disclosed in U.S. Pat. No. 5,180,108 and U.S. Pat. No. 6,994,274. The '108 patent also discloses that the smaller engine may be operated from the fuel supply for the truck engine. However, the use of a separate smaller engine to operate the distribution pump for the liquid chemical spraying system requires significant additional maintenance of the smaller engine to assure that it is dependable every day of use. The additional engine also adds significantly to the cost of the system and increases the consumption of fuel.